Former Wallaby Berrick Barnes believes rugby has a bright future in Japan, but he's unsure if it includes the Sunwolves.

Sunwolves player Harumichi Tatekawa attempts to breach Rebels defence

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Barnes has one more season to run on his contract with Top League side Panasonic Wild Knights, who he first joined back in 2013.

The ex-Queensland and NSW back said he has loved every moment since moving to Japan and believes the country will host a successful World Cup in 2019.

But what Japanese rugby looks like beyond then remains to be seen.

The Tokyo-based Sunwolves - who have won just three matches since their inception - will join the Australian conference in Super Rugby this year and Barnes believes they will improve after bolstering their squad with a number of key foreign imports.

However, the franchise faces a constant "juggling act" given the financial strength of Top League clubs, which are bankrolled by major companies like Panasonic, Suntory, Toyota and Honda.

"The money's not in the international game in Japan. It's not in the JRFU, it's within the companies," Barnes said.

"Companies pay their players and they're effectively paying their Sunwolves deal. It's that push and pull.

"Most of them are really generous and give their players and I know we do at (Panasonic), we want our players to go forward and experience that stuff. But it's kind of hard.

"But coming into a World Cup, everyone's got on board to know that (the Sunwolves need) success ... (it's) similar to what they do in New Zealand, everyone knows the All Blacks is the top brand so they've got to try and push the resources into that first and foremost."

The Sunwolves' very existence is up in the air - along with the rest of Super Rugby, which could face dramatic changes when the current broadcast deal for the competition expires in 2020.

"I don't know what the future is ... after the World Cup some big decisions need to be made about where the future's going to be heading in the southern hemisphere and what the product is and where it goes," he said.